In a SAGD (Steam Assisted Gravity Drainage) method for recovering bitumen or viscous oil from a hydrocarbon-containing formation, a horizontal injector well is drilled relatively high in a region of the formation under development. A parallel horizontal production well is drilled low in the region of the formation under development. The production well has a horizontal portion typically situated 5-6 meters directly below the horizontal portion of the injector well, and parallel thereto, and which like the horizontal portion of the injector well, extends into the hydrocarbon-containing layer. Steam is injected into the hydrocarbon formation via the horizontal portion of the injector well, and oil within the formation which becomes heated and thereafter becomes mobile, by force of gravity and/or pressure drains downwardly in the formation where it is collected in the horizontal portion of the production well and produced to surface.
Typically, the injector well and the collector well of a SAGD well pair are drilled from one end of a development region within the formation, and typically from the same well pad at one end of such development region.
Where a large formation is being exploited, numerous SAGD well pairs comprising parallel, vertically aligned injector and producer wells are aligned in side-by side juxtaposed position, with each producer well being positioned vertically below a paired injector well.
Large capital costs are incurred in not only drilling the injector and producer wells, but also in obtaining the necessary equipment, such as steam generating equipment and piping, for such SAGD method of recovery.
Clearly, therefore, in light of these large capital costs, it is advantageous to maximize oil production from such wells to ensure the greatest return on investment, and further recover such oil as quickly as possible once these capital costs have been incurred to thereby obtain the quickest return on investment.
Accordingly, a real need exists to improve upon the existing SAGD method to realize these objectives.
In addition, problems may arise in existing SAGD well pairs during the life of such wells, such as “sanding in” of production wells, or leakage of steam from the injector wells directly into the production well without flowing firstly through the desired areas in the development regions which are desired to be heated to mobilize oil therein. Both of these problems significantly reduce the volume and recovery rates of oil from such wells and/or may possibly prevent further recovery of economic amounts of oil even though a significant amount of heavy oil may still remain in the region of the formation under development.
Accordingly, a real need further exists for an effective manner of recuperating or rejuvenating production wells in SAGD well pairs which are not operating to maximum potential, in order to recover as much of the oil from the region under development and avoid loss of invested capital.